Headless set screws with center of gravity located so that screw will be properly oriented



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C.. O. v HEADLESS SET SCREWS WITH CENTERv OF GRAVITY LOCATED SO THAT SCREW WILL BE PROPERLY ORIENTED Filed June 9, 1955 5 Sheets-Sheet 3 INVENTOR.

Mafch 17, 1959 H x c. 0. BROWN 2,877,680

EADLESS SET SCREWS WITH CENTER OF GRAVITY LOCATED SO THAT SCREW WILL BE PROP ERLY ORIENTED Filed June 9, 1.955

5 Sheets-Sheet 4 INVENT March 17, 1959 c. 0. BROWN 2,877,680

. HEADLESS SET SCREWS WITH CENTER OF GRAVITY LOCATED so THAT'LSCREW WILL. BE PROPERLY ORIENTED Filed June 9, 1955 5 Sheets-Sheet 5 INVENTOR.

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United States Patent '0 HEADLESS SET SCREWS WITH CENTER OF GRAV- ITY LOCATED SO THAT SCREW WILLBE PROP- ERLY ORIENTED Calvin 0. Brown, Bartlett, Ill., assignor to Set Screw &

The invention herein disclosed is concerned with the construction of certain types of headless set screws, adjusting screws, studs and like items, especially those of the smaller sizes, /2 inch in diameter and less, to enable such items to be fed and inserted or set in work articles or packaged or otherwise utilized in an automatic or semiautomatic operation as by mechanisms such as that disclosed and claimed in my co-pending application Serial No. 514,299, filed June 9, 1955. In a more particular sense the invention is concerned with a special construction for headless set screws and other items of a related or similar nature, which will permit such screws or other items to be oriented or placed in the same axial and end relationships without materially altering the normal structural or functional characteristics-of such screws or other items. The invention will be disclosed in its application to headless set screws which may serve as an excellent example.

Headless set screws, although they may have dissimilar ends as where one end is of slab form orhas a slot or socket or is otherwise prepared so that the screw may be engaged by a torque applying means, and the opposite or lead end has a dog, cone, cup or other form, for abutting engagement with some object, are usually very diflicult, tedious and time consuming to handle or manipulate as where they must be picked up, oriented, entered in a threaded bore, and set or screwed into the bore'with some appropriate tool such as a screw driver or socket or hex-wrench or key. The problem is aggravated no end when small items such as some of the smaller set screws of say, one-half inch or less in diameter, are being handled, but by employing machines such as that of the. above noted co-pending application many headless screws and like items, whether large or small in diameter and whether long or short in length as compared to their diameter, may readily be oriented and set or otherwise used in a very rapid and eflicient manner.

However, where such headless screws while being what may be termed longitudinally asymmetric, i. e., have different end forms, are not also gravimetrically asymmetric, i. e., do not have their centers of gravity unequally located as respects their axial lengths, by reason of some particular normal or standard characteristic, or, where headless screws or studs and the like have diameters (crest or major) equal to or substantially equal to or greater than their axial length or the axial length of the thread, it becomes very diificult to assure their orientation by a machine such as that mentioned above or by any other presently known machine.

Consequently, one of the primary objects of the invention is to provide a construction for headless set screws, studs, adjusting screws or like items which are not normally gravimetrically asymmetric or which by reason of some other characteristic such as a diameter substantially equal to or greater than its length cannot readily be caused to assume predetermined orientation, as will enable such items -to-be automatically oriented withprecisio'nand 2,877,680 Patented Mar. 17, 1959 in! speed and fed and set, as by the machines mentioned, ,or otherwise utilized in their oriented condition or state.

Many other objects, as well as the advantages and uses of the invention will be or should become apparent and understood after reading the following description and claims and after viewing the accompanying drawings in which Fig. 1 is a perspective view of a fragment of a vibratory hopper bowl with'one form of roller type orienting device connected therewith, whereby screws of the invention when placed in bulk and haphazard arraywithin the hopper bowl may be fed in single file succession and in axial alignment from the bulk or mass within the hopper to the roller orienting mechanism, oriented so that corre sponding ends are arrayed in the same direction, and fed in such oriented condition to some place of disposal;

Fig. 2 is atop plan view of the mechanism shown in Fig. 1, the view also showing a motor for driving the orienting rollers and the motor supporting means;

Fig. 3 is a large scale, more or less diagrammatic, view through the orienting rollers shown in Fig. 2, showinga screw in position between the rollers, the view being taken substantially along the section line 33 of Fig. 2 looking in the direction of the arrows, the scale of the screw being 10 times actual size in the original patent drawings;

Fig. 4 is a large scale view of a slotted head cup point set screw of the type diagrammatically illustrated in Fig. 3, the screw represented being a No. 8-32 x A NC, slotted head cup point set screw, the scale being 20 times actual size in the original patent drawings;

Fig. 5 illustrates a set screw having a flat point and a slotted opposite or torque applying end for engagement by a screw driverblade, the screw being specially formed to enable it to be oriented by roller orienting mechanism of the type shown in Figs. 1 and 2 hereof, the screw being shown in its normal relation to the orienting rollers just before tipping or turning under the influence of gravity to a position where its axis will be substantially at right angles to the axial position shown;

Fig. 6 is an enlarged detail view of the specially formed flat end set screw shown in Fig. 5, the screw number or nominal size being A-ZO NC, A" long shown ona scale of four times actual size in the original patent drawings;

Fig. 7 is a view corresponding to that of Fig. 3 illustrating a screw of a modified form of the invention, the number or nominal size being 8-32 NC, A" long, the scale being ten times actual size in the original patent drawings;

Fig. 8 is a detail side view of the screw shown in Fig. 7 on a scale of twenty times actual size in the original patent drawings;

Fig. 9 shows still another screw modification as it appears between the orienting rollers, the number or nominal size of the screw being 4 -48 NC, long, the scale being ten times actual size in the original patent drawings;

Figs. 10, 11 and 12, respectively, are plan views of the top or tool engaging end and the bottom or lead or point end, and a view in side elevation, of the screw of Fig. 9, the scale being the same as that of Fig. 9; and

Fig. 13 is a detail view in side elevation of the screw of Figs. 9, 10, 11 and 12 but taken from a positionremoved aboutthe screw axis from the position of the view of Fig. 12, the scale being twenty times actual size in the original patent drawings.

It may be well to observe at this time that it is by reason of the substantial importance or critical nature of relative dimensions and the relatively small dimension quantities involved in the invention and set screws and similar items to which the invention is applicable, that the screws rep-. resented as embodying the invention and the 'rollersb'y which such screws may be oriented have been illustrated to scale and on the large scales stated above. Those skilled in the art may have a more ready appreciation of the significance of the invention features and the results attained thereby through such illustration.

. The combined bowl hopper and roller orienting mechanism illustrated in Figs. 1 and 2 and now to be described are part of the subject matter disclosed and claimed in my co-pending application Serial No. 514,299, filed of even date herewith. They are shown for the purpose of assuring a clear understanding of the mannerin which the invention makes it possible to orient certain types and sizes of headless set screws and the like. Not shown in the views is the vibrator mechanism by which the hopper bowl, the orienting rollers and the set screws or other articles which are to be oriented, are vibrated to cause the work articles (the set screws in this instance) to move to the outside of the bowl bottom, up the ramp or track on the bowl wall, and onto and along the roller orienting mechanism, one satisfactory type of such vibrator mechanism being fully disclosed in Spurlin Patent No. 2,696,292, dated December 7, 1954, and also disclosed in the aforesaid copending application Serial No. 514,299. While vibration of the orienting roller mechanism and of the screws to effect orientation of the screws is not always necessary, it has been found to be uniquely effective in facilitating the orientation especially with certain types and sizes of screw. Also, while a vibratory type of feed such as that of the above noted Spurlin patent is particularly effective in combination with an orienting mechanism of the character of that herein described, other means for feeding and/or vibrating the screws to the orienting rollers may be employed.

The circular bowl generally designated has a conical interior bottom surface 16 upon which the screws or other articles to be oriented are received. This formation of the bowl bottom facilitates the flow of screws outward toward the bowl side wall 17 which is so formed as to provide a ramp or conveyor track 18 in the form of a conical spiral the radius vector of which increases constantly from the juncture of the bowl interior bottom surface 16 with the bowl side wall 17 to the upper edge or rim 19, where the spiral track merges with a track portion 18 extending tangentially of the bowl. The side wall 17 may be cut away or recessed as indicated at 20 and including a section beneath the tangential portion 18' of the track so that such track portion will overhang or jut over the orienting roller mechanism to be described. The transverse or radial width of the track is made only slightly greater than the diameter of the screws or other articles to travel therealong so that those screws or other articles will be forced into single file automatically with their axes aligned in the direction of travel but in some cases with their axes transverse to their line or direction of travel, the track contour aiding in this function.

The hopper bowl is supported through springs upon a massive base member and an electromagnetic motor produces impulses which so react upon the hopper bowl and the screws or other articles within it as to cause screws to move radially outward to the bowl side wall and thence in a circular or spiral path onto the spiral track 18, and thence up that track onto and outward to the end of the tangential track portion 18 from which the screws drop in succession onto the orienting rollers next to be described. The means for supporting and vibrating the bowl and causing the screws or other articles to travel in the paths stated are not shown since reference may easily be had to the above noted Spurlin patent.

A pair of similar, conically tapering orienting rollers 21 and 21 underlie the tangential end portion 18' of the track with the center of the track directly above and intermediate between the adjacent large end portions of the rollers. Each of the rollers 21 and 21' in this embodiment is conically tapered to the same degree which, inthe example given is 1 45 and over the same length as the other roller and corresponds to the truncated portion of a right circular cone having an apex angle 3 30', as will be appreciated. Each roller is mounted for rotation about its axis between a pair of adjustable screw trunnions 22 and 23 which are carried in alignment with one another by the arms 24 and 24' of a yoke 25. That end of each roller which is adjacent to the terminal end portion 18' of the hopper bowl track is reduced in diameter and provided with a circumferentially extending groove which is to serve as a pulley or sheave for a belt 26 which transmits power to the rollers from a pulley or sheave 27 mounted on the shaft of a small synchronous electric motor 28 carried by a bracket 29 which may be secured to the outside wall of the bowl hopper or by the bracket (not shown) by which a base plate 31 carrying the roller yokes and rollers is also supported on and by the side wall of the bowl hopper. Intermediate of its ends but substantially closer to the small end than to its large'end, each roller is circumferentially grooved, as indicated at 32, in a manner, to an extent and for a purpose to be made clear hereinafter.

Each of the yokes 25 is mounted, for lateral and longi tudinal adjustment upon the base plate 31 by means of a pair of cap screws 33 the shank of each of which passes through a bore in the yoke and is threaded into the base plate 31, the bores being of a substantially greater diameter than the shanks of the cap screws so that upon loosening these cap screws the yokes (and rollers) may be shifted relative to one another to effect adjustment in substantially every direction in a plane parallel to the base plate 31. As indicated by the arrows in Figs. 3, 7 and 9, the belt drive is arranged to rotate both rollers and each in such direction that a point on the surface of each as it approaches a corresponding point on the surface of the other will move upward. Preferably, the roller assembly, including the yokes 25 and the base plate 31, is so mounted on the bowl as to be adjustable vertically and also about a horizontal axis normal to a vertical plane parallel to the tangential portion 18' of the track and since this will be clear to anyone skilled in the art and, as such, is not part of the instant invention, it is not illustrated in detail herein.

While the tapered rollers 21 and 21' are preferably so disposed that their axes lie in a horizontal plane, those axes converge toward one another from the large diameter ends of the rollers to their opposite or small diameter ends to include an angle of 3 30 equal to the sum of the taper angles of the rollers, that is, to include an angle equal to the apex angle of the right circular cone of which each roller is a truncated part. Thus the lines of intersection of adjacent surfaces of the pair of rollers 21, 21, with the horizontal plane containing the roller axes, will be parallel to one another and, since the rollers normally will be spaced apart throughout their coextensive lengths, this spacing will provide a slot of uniform width throughout their coextensive lengths ex cept for the grooves 32. The grooves 32 not only are located closer to the small ends of the rollers than to the large or opposite ends but are spaced at the same distance from the small end, have the same contour length as measured along the tapered surface of the roller, and have the same depth as measured normal to the roller axis. Consequently the grooves 32 may be characterized as complementary to one another.

Normally the rollers will be so spaced that the mini mum width of the slot between them as defined by the lines of intersection of the horizontal plane containing the roller axes with the adjacent side wall surfaces of the rollers will be several thousandths of an inch less than the minimum allowable crest diameter of the standard thread of the standard headless screw of a given size and fit class to be received upon the rollers for orientation purposes. In practice it has been found that a spacing of between 0.002" and 0.005" less than the minimum, allowable major or crest diameter of a standardthread of a given fit class and nominal size of screw to be oriented, or in certain types of lock threadedscr'ew such asthose described and claimed in the copending application'of Brown et al., Serial No. 485,630, filed February 2, 1955, and now abandoned, less than the minimum crest or major diameter of an oversize thread portion, is entirely satisfactory. Ordinarily in spacing the orienting rollers, a decrease below the minimum allowable crest diameter of the particular screws to be oriented of from 0.002 to 0.003 will be found to be sufiicient and desirable for the less the different between the slot width and the allowable minimum major or crest diameter of the screw or other article being oriented, the more closely will tolerances be held in the final oriented product since any undesirably undersize screws will drop through the slot and be rejected before reaching the grooves.

The drawings represent headless set screws of different sizes and show two different styles of lead, point or entering end, and two styles of driving or torque tool engaging end, either slotted or hexagonal socket. All of the screws illustrated except insofar as modified in manners' and to the extents described hereinafter, conform to established standards for headless set screws and the like 'set forth in Screw-Thread Standards for Federal Services, 1944, Handbook H-28, U. S. Department of Commerce, National Bureau of Standards, and the 1950 Supplement to said handbook. Following the standards stated and except as modified the screw chosen for illustration in Figs. 3 and 4 is an 8-32 NC, 7 long in actual size; the screw shown in Figs. 5' and 6 is a standard %20 NC, long in actual size; the screw shown in Figs. 7 and 8 is an 8-32 NC, A long in actual size, and the screw shown in Figs. 9 to 13, inclusive, is a 18, NC, 1 long in actual size. The rollers employed for orienting any and all of these screws may have a large end diameter of a small end diameter of A", a length measured from the end of the large diameter to the end of-the small diameter of 1%" and preferably are driven at aspeed of about 260 R. P. M. The width of the slot between the rollers will be determined as above stated.

Each of the roller grooves 32 may have an arcuate bottom cut on a radius of 0.003 to 0.004" greater than the radius of the maximum allowable major or crest diameter of screws of the nominal size and fit class to be oriented when the rollers are spaced at from 0.002 to 0.003, both limits inclusive, less than the minimum allowable major or crest diameter of such screws. Thus the arcuate bottoms of the grooves will be concentric with the axes of the screws which pass between the'rollers through the grooves with an average radial clearance of from 0.003 to 0.004" along the arcuate length of each of the opposed grooves. However, some screws have characteristics such as length and location of center of gravity which may call for a construction wherein eachgroove is elongated in the direction of the roller axisalthough made no deeper than will give the specified clearance of from 0.003 to 0.004" from the crest of the thread of the screw.

In thepreferred arrangement of the rollers and yoke arms, the clearances between the yokes and their arms and the ends and outer sides of the rollers will be such that no screw being oriented will pass therebetween to jamb the apparatus. Any screws of oversize, either of diameter or of length, such as would prevent the screw from passing through the grooves, will pass over the grooves and off of the smaller end portions of the rollers to someplace of disposal. Similarly, should the screws feeding along the rollers fail for any other reason to feed downward through the opening provided by thegrooves 32 as when screws are feeding to the rollers fasterv than disposal can be made of them, they may overflowthe roller ends and by a trough or other means (not shown) may be fed back to the hopper bowl for.

6 recycling. Screws passing downwardthrou'gh the grooves 32 may be received into the tube 34 for delivery in oriented'condition to any desired place. The diameter of the tube 34 will be such as will permit the screws to slide or fall freely therein but without canting or turning end for end as will be appreciated.

The vibrator mentioned above causes the screwsto flow out of a mass of such screws which may have been dumped into the hopper bowl in haphazard array, the screws moving to the junction of the bottom and side walls of thehopper bowl and moving therearound to and climbing the spiral ramp or track up the bowl wall 'in a more or less steady and continuous stream in single file to drop, one after another, upon the orienting rollers 21, 21'. If the track is of such width and conformation as is preferable the screws will travel up thetrack in single file. Long screws may travel end to end but in disordered or hit-or-miss array insofar as their lead and tool engaging (slotted, socketed or other) ends are concerned, some screws traveling with their lead ends first and some with their tool engaging ends first, the axes being as nearly aligned as the curved track willpermit. If the screws are square, that is, have a'diameter equal to or substantially equal to their length or if the diameter is greater than the screw length, then, while the screws may travel up the track in single file, they may assume almost any position, i. e., with their axes in almost any direction. After the screws fall upon or, rather, between the rollers they are either oriented before they reach the roller grooves and drop into tube receiver 34, if they are screws of the forms of the invention shown in Figs. 1, 2, 3, 4, and 7 to 13, inclusive, or, if they are of the form shown in Figs. 5 and 6 (a form also disclosed in said copending application Serial No. 514,299), the screws will not be oriented until they reach the grooves 32.

While the roller axes in the machine illustrated in Figs. 1 and 2, are in a horizontal plane, their taperprovides a slight downhill path from their large diameter ends adjacent to the end of the track 18' to'their. opposite ends so that with the rollers rotating, the screws riding along between them will move steadily toward the orienting grooves 32. Since the rollers are supported upon the hopper bowl which is being so vibrated as to cause the screws to feed up the track and onto the rollers, the same or components of such vibration augment the action of gravity and the rotation of the rollers in moving the screws along their roller supported path. As explained in said copending application Serial No. 514,299, certain standard types or forms of set screws and the like without change in structure'or'dimensions may readily be oriented by the mechanism above described but other'types or forms are not susceptible of orientation or certainty of orientation by such mechanism except when constructed or modified in a manner such as disclosed herein.

Standard or normal set screws of the square or substantially square type above mentioned, for instance, standard-set screws of a nominal size 8-32 NC, 5 1 long are not successfully oriented by a roller mechanism of the character described above, partly perhaps, because some of the screws are quite as apt to ride the rollers with their axes transverse to the path of travel therealong as with their axes parallel to and in line with the path of travel, and, perhaps, partly because the center ofgravity of such screw is either at or so close to'the center of the threaded length that there is not sufiicient unbalanced condition such as would cause the screws to tilt at the edge of the orienting grooves and fall therethrough in oriented relationships. However, when such screws are modified as shown in Figs. 3 and 4, they at once become orientable by the mechanism described. This modification consists in trimming back the thread crest i. e. reducing the thread major or crest diameter, over such length of the thread from one end or the other as may be necessary to bring the'center of gravity of the screw within the axial length of the reduced crest diameter portion, the reduction being sufiicient to permit such axial length of the screw to pass through the narrow slot between the rollers although the remainder of the screw will not pass by reason of retention of the standard or normal major or crest diameter for one or. more thread turns (at least one complete turn) between the reduced thread turn crest portion and the opposite end of the screw. Usually the reduction in crest diameter will be effected at the lead or point end of the screw rather than at the end to be engaged by a torque applying tool but it ,is possible to have satisfactory results by reducing the thread major diameter at the latter end if desired.

The screw 40 shown in Figs. 3 and 4 is provided with a cup point 41 at its lead or entering end and a slot 42 at its other or torque tool engaging end. As stated above, except for the modification effected to make the screw susceptible of orientation by the roller mechanism disclosed, the screw is a standard number 8-32 NC, 05 long, the allowable thread crest or major diameter of which for a class 2 fit may lie within the range of 0.1640 inch maximum and 0.1586 inch minimum. It is, of course, preferable that the tolerance between the maximum and minimum allowable major diameters for such screw be held as low as possible with variation toward the higher allowable major diameter preferable to variation in the other direction.

With the usual or standard slot and cup formation for the screw number and size given above, it has been found that the center of gravity lies at a point somewhat more than half of the distance from the slotted end to the cup end so that a reduction in or truncation of the thread crest along or for from two and one-half to three turns of the thread as indicated at 43 will include the center of gravity within the length of such reduced portion measured along the screw axis. Of course this reduction tends to move the center of gravity toward the slot end of the screw but the amount of such change of position will be immaterial so long as the center of gravity lies within the reduced crest length or the distance from the center of gravity (if the center of gravity lies within the normal or untruncated length of the threaded portion) to the adjacent truncated portion, is less than the length of the groove. In screws made in accordance with the example under consideration in Figs. 3 and 4, the standard or normal maximum and minimum major diameters for thread turns 44 were held to 0.1610" and 0.1590", respectively, and the crests of turns 43 or for approximately one-half of the screw length, a distance of 0.093", was reduced to a diameter Within tolerance limits of 0.1530 maximum and 0.1510" minimum or to approximately 70% thread based on the assumption that the mean of the maximum and minimum standard major diameter limits, 0.1610" and 0.1590, produced a 100% thread. It has also been found that crest diameter of the reduced turn portion may be reduced to such extent as will leave as little as a 50% thread but such reduction will rarely if ever be necessary.

The resulting screw product oriented in a most satisfactory manner, each of the screws when dropped onto the rollers 21, 21 in any axial position, quickly becoming oriented to the position illustrated in Fig. 3 and also in Figs. 1 and 2, thereafter traveling to the aperture provided by the grooves 32 and dropping therethrough into the tube 34 in their oriented state. Screws which were undersize, that is, had a maximum crest diameter over the normal or standard turns 44 less than the width of the slot between the rollers, dropped through that slot before reaching the grooves 32 and were rejected. Similarly, oversize screws, that is, screws having a diameter greater than would pass through the grooves, rode on off the small end of the rollers and were rejected. The rollers therefore serve both as an orienting and as 8 a selecting, grading, classifying or inspecting apparatus.

The screw illustrated in Figs. 7. and 8 differs from the screw ofFigs. 3 and 4 in two primary respects namely, first, the crests of all thread turns except that of one full turn, designated 81, which is closest to the torque tool engaging end of the screw, are cut down or truncated and, second, the truncation or reduced diameter has effected a reduction of the thread by an amount proportionately somewhat greater than the reduction of thread turn crests in the screw of Figs. 3 and 4, a reduction to a 50% thread being indicated. In addition to the foregoing difierences and the fact that the screw is longer than that shown in Figs. 3 and 4, the juncture between the truncated turns and the one standard or normal turn is bevelled at the relatively low angle of 12 as indicated. Screws prepared in this manner for orientation orient very effectively.

The screw designated in Figs. 9 to 13, inclusive, carries a class 3 fit thread formed by a centerless thread grinding operation after which flats 131 are ground or otherwise formed at diametrically opposite sides adjacent to the lead end of the screw instead of but for the same purpose as the circumferentially extending crest reductions of the earlier described embodiments. The rotating and vibrating motions of the rollers and the screws falling or riding upon them and partaking of some or all of the motions of the rollers, cause the screws to assume positions as indicated in Fig. 9 (or, as indicated in Figs. 1 and 2) in which positions the flats on the thread crests will permit the lead ends of the screws to project through the narrowest part of the roller slot. The screws then travel along the slot to the grooves 32 which permit them to drop through into the receiving tube 34.

Screws of the size and type of screw 130 which, as will be recalled, is & in diameter and 4 long, are what may be termed square screws which here are provided with flats reducing the thread crest over a part of the axial length at opposite sides. It has been found that when the screws have oppositely disposed flats, as described herein, they may be successfully oriented. In the example shown on detail in Fig. 13 the minimum depth of reduction of the thread crest to form each flat 131, as measured along a radius of the screw normal to the fiat, preferably will be such as to reduce the radial distance from the flat to the axis by an amount from 0.0045" to 0.0055" below one-half of the minimum allowable major diameter for a standard thread of the particular screw number or nominal size, class 3. While the reduction is shown at both sides of the diameter of the screw the reduction may be at one side only but in such event the amount of reduction must be sufficiently below the width of the slot between the rollers as to permit the lead end of the screw to pass through the slot as shown in Fig. 9 of the drawing. g

The screw illustrated in Figs. 5 and 6 is the same as that shown in Fig. 14 of said copending application Serial No. 514,299. By reason of its length the screw 60 in stead of traveling along between the rollers with its axis vertical or substantially vertical as other screws described hereinabove will do, will travel along the rollers with its axis substantially horizontal or substantially parallel to the plane containing the roller axes. crests of several of the thread turns at the lead end are reduced so that the center of gravity of the screw in effect is shifted to lie between the center of that portion of the threaded length which remains unreduced or untruncated and the lead end of the screw, the screw when it reaches the orienting grooves 32 will tip or tilt so that its lead end will be down and its tool engaging end will be up to permit the screw to drop under the action of gravity down through the grooves into the receiving tube;

therebelow. As indicated at 61 in Fig. 6 approximately three turns of the thread at the lead. end have been truncated. Preferably this truncation will-be in the range However, if the asv'aeao of from 0.006" to 0.012", both limits inclusive, on the diameter.

While I have illustrated and described a presently preferred form of the invention and several embodiments thereof, it is susceptible of many variations and changes without departing from the invention spirit and the scope of the appended claims.

I claim:

1. As an article of manufacture, a headless screw such as a set screw having a substantially cylindrical body, one end of the body being recessed for engagement by a torque applying tool to effect rotation of the screw about its axis, a plurality of turns of uninterrupted thread on the body about the axis thereof, said thread throughout all turns thereof having substantially uniform pitch,

flanks, and minor diameters within allowable dimension limits for a standard screw thread of the screw number or nominal size and fit class, at least one turn of the thread at one end thereof having a major diameter within the allowable major diameter dimension limits for a. standard screw thread of the said screw number or; nominal size and fit class, all other turns of the thread having a major diameter less than the major diameter of the turn at said one end, the reduced major diameter providing at least a 50% thread the center of gravity of the screw being located within that axial length of the screw carrying said other turns.

2. As an article of manufacture, a headless screw such as a set screw recessed at one end for engagement by torque applying means for rotating the screw about the axis thereof, a plurality of turns of uninterrupted helical thread on the screw about said axis, at least a majority of consecutive turns of said thread beginning with one terminus of the thread having substantially uniform pitch, flanks, and minor diameters within the allowable dimension limits for a standard thread of the screw number or nominal size and fit class, the major diameter of the thread for at least one turn beginning with the other terminus of the thread being at least equal to the minimum allowable major diameter for a standard thread of the screw number or nominal size and fit class, the thread et e n said e turn nd d 1 erm n s o he 10 thread having a substantially constant major diameter less than the major diameter of said one turn, the reduced major diameter providing at least a thread, the center of gravity of the screw being located between said one turn and said one terminus of the thread.

3. As an article of manufacture, a headless screw such as a set screw recessed at one end for engagement by torque applying means for rotating the screw about the axis thereof, a plurality of turns of uninterrupted helical thread on the screw about said axis, at least a majority of consecutive turns of said thread beginning at said one end of the set screw having substantially uniform pitch, flanks, and minor diameters within the allowable dimension limits for a standard thread of the screw number or nominal size and fit class, the major diameter of the thread for at least one turn adjacent to said end of the set screw being at least equal to the minimum allowable major dimeter for a standard thread of the screw number or nominal size and fit class, the thread turns between said one turn and the other end of the set screw having a major diameter less than the major diameter of said one turn by an amount within the range 0.006" and 0.012" both limits inclusive, the center of gravity of the screw being located between said one turn and said other end of the set screw, the reduced major diameter providing at least a 50% thread.

References Cited in the tile of this patent UNITED STATES PATENTS 1,609,994 Ellis Dec. 7, 1926 1,685,899 Andrew Oct. 2, 1928 1,760,441 Risser May 27, 1930 1,863,314 Phelps et al. June 14, 1932 2,021,704 Thatcher et al Nov. 19, 1935 2,096,937 McManus Oct. 26, 1937 2,352,540 Hanneman June 27, 1944 2,3 83,270 Niederer et al Aug. 21, 1945 2,421,181 Batchelder May 27, 1947 2,555,243 Parker May 29, 1951 2,574,677 Wieland Nov. 13, 1951 2,531,635 199 M tv 1 3 

